High temperature heating

ABSTRACT

A process and device for high temperature heating of objects having extended surfaces. At least one group of separated plasmas jets is used which are created by a high current circulating between sets of cathodes and an anode having orifices with which the cathodes cooperate.

XFQ 396609630 I United States Patent [151 3,660,630 Sunnen et al. 451 Ma 2, 1972 [54] HIGH TEMPERATURE HEATING References Cited [72 Inventors: Jean A. F. Sunnen, Waterloo; Henry R. P. UNITED STATES PATENTS J- Schollmflker, BruXeileS, both of e g u 3,205 333 3 19 5 Sunnen 2 9/ 21 p [73] Assignee: La Soudure Electrique, Procedes Arcas, 3,050,616 8/1962 8 R Andertecht, Belgium 3,466,487 9/1969 Davis etal. ..219/121 EB F'l d: 2 ,l 7 [22] l e Mar 3 9 0 Primary Examiner-C. L. Aibritton i PP Noll 2 36 Assistant Examiner-J. G. Smith Attorney-Jackson, Jackson and Chovanes [30] Foreign Application Priority Data Mar. 3], 1969 Belgium ..72l46 [57] ABSTRACT A process and device for high temperature heating of objects [52] U.S.CI ..219/76,2i9/l2i P havingextended surfaces. At least one group of separated Cl plasmas jets is used which are created by a high current circu- [58] FieldofSearch ..219/12] R, l2iP,i2lEB,26

iating between sets of cathodes and an anode having orifices with which the cathodes cooperate.

4 Claims, 12 Drawing Figures .I'IIGII TEMPERATURE HEATING A wide variety of plasma generators is known which operate on direct current as well as on alternating current, with an electric arc striking between two or more electrodes which are generally coaxial, the are being expelled as a flame of circular or generally circular cross section. In all of these prior art generators, the plasmas have a small cross section which concentrates a very large amount of heat energy.'These devices are valuable when considerable energy must be applied 10- cally. There are, however, many cases in industrial heating where the heating must be applied over a much larger area.

The present invention relates to processes and apparatus for heating to high temperature objects having extended surfaces. In the invention a plurality of separate plasmas are created and distributed so as to apply the heating over a wide area.

The multiplicity of plasmas are preferably created by a large current which is circulating between at least two cathodes and at least one anode provided with orifices or plasma constricting nozzles, each one of which cooperates with one of the cathodes. The plasma jets are propelled from the orifices or nozzles by a suitable gas, desirably an inert gas such as argon, helium or nitrogen.

The single anode or multiple anode device, preferably made of copper or silver, is vigorously cooled by a circulating fluid such as water, and the cathodes are also vigorously cooled.

The following description and the accompanying drawings show by way of example only, various embodiments of the invention which will provide a precise understanding of it and emphasize its advantages.

FIG. 1 is a schematic front cross section of one embodiment of the invention. I

FIG. 2 is an end elevation of the device of FIG. 1, partly in section on the line II-II thereof.

FIGS. 3, 4, 5 and 6 are electric circuit diagrams including electrodes in section, showing variations in the procedure for controlling the current feeding a device of the invention.

FIG. 7 is a perspective of a twin embodiment of the invention.

FIG. 8 is a diagrammatic cross section of the device of FIG. 7 on the line VIII-VIII.

FIG. 9 is a diagrammatic perspective of another twin embodiment of the invention.

FIG. 10 is a perspective of a further device embodying the invention.

FIG. 11 is a radial section of the device illustrated in FIG. 10.

FIG. 12 is a cross section of a further variation in the device ofthe invention.

The device shown schematically in cross section in FIG. 1 consists of an elongated anode 1 which is preferably made of copper and provided with a plurality of aligned parallel orifices or nozzles 2. Cathodes 3 are aligned along the axes of the nozzles 2. The cathodes are preferably made of tungsten, and are cooled as well known. The cathodes are mounted on a non-conductive common plate 5 and they pass through chambers 6 which communicate with the nozzles 2. A propellant or plasmagene gas such'as argon, helium or nitrogen is supplied to the chambers 6 by channels 7 provided in the walls separating these chambers. The channels 7 are connected to means for-supplying the gas and for rendering the output of each plasma separately adjustable.

The cathodes 3 are electrically insulated from the anode l by insulating plates 8.

The anode] is connected to one of the two terminals of a source 40f direct current by a conductor 9 and so forms a multiple anode if the connection is properly made to the positive terminals. The anode is further provided with inlets 11 and outlets 12 for cooling water circulating between the nozzles 2, as shown in FIG. 2.

On the other hand, the cathodes 3 are connected in parallel to a conductor 10 which is connected to the other terminal of the power source 4, so that the current in each individual circuit can be independently adjusted for the individual cathode.

' As a result arcs strike between the appropriate cathode and the anode and hot gases are expelled from the nozzles 2 in the form of plasmas or flames 13 as a result of the circulation of the electric current and the pressure of the plasmagene gas sent into the chamber 6.

In order to obtain the adjustment of the current passing through each arc, an individual source of direct current 14 can be used for each cathode as shown in FIG. 3, the source being connected at one side to the cathode and at the other side by a common connector 9 with the anode. On the other hand, a single power source 15 (FIG. 4) can be used with the addition of individual adjustable resistors 16 between the source 15 and each of the cathodes 3.

In another embodiment, as shown in FIG. 5 all the cathodes are at the same potential and the nozzles 2 of the multiple anode are electrically insulated from each other by insulating spaces 17 surrounding the nozzles. Each of these anodes is separately connected to an individual source of direct current 14 as in FIG. 5 or to a single source 15 through individual resistors 16 as shown in FIG. 6.

The initial striking of the arcs can be caused by momentarily bringing the cathodes into contact with the respective anodes and then separating them. It is, however, preferred to use a high frequency pilot spark to start the arcs. If the high frequency generator is powerful enough, several arcs may be ignited simultaneously. However, a low power high frequency generator may be preferred to minimize radio interference, and it is connected successively between each cathode and the multiple anode in turn to ignite the arcs in a predetermined order. The electric current and the gas output may be adjusted for each nozzle to control the power generated by the arc and the temperature and the composition of the gas ejected by each nozzle.

The multiple anode may consist of a cooled bar of copper or silver pierced, for example, every 10 mm. by an orifice having a diameter of 2 to 8 mm., the power of each are being for instance lO to 20 kw. with enough room to locate I00 nozzles in 1 meter of length and so to generate 1,000 to 2,000 kw. in the form of parallel plasmas or flames, creating a current of plasma at very high temperature, arranged in multiple jets.

Such multiple plasma devices are useful, especially for high temperature heat treating, such as spraying refractory materials, nitriding, annealing, and quenching when the work is in motion and has a large area in contact with the plasma curtain.

By connecting several sets of plasma flames of this character in parallel, one can obtain panels which make it possible to spread enormous power, of the order of 50,000 to 100,000 kw. Such panels may be used as sources oflight radiation for radiant heaters or floodlight high power projectors.

FIG. 7 shows work 33 being treated by one of the installations under discussion. In this device two multiple twin anodes 18 and 19 are connected respectively to the terminals 20 and 21 of the secondary winding of a transformer 22 by conductors 23 and 24, and are arranged in two batteries with corresponding cathodes 25 and 26. The cathodes 25 are connected electrically each to one terminal of an individual power source 27 of direct current, while the other terminals are connected to the common anode 18 by reason of a common conductor 29. The cathodes 26 are connected each in a similar manner to one terminal of an individual power source 28 of direct current, while the second terminal is connected t0 the common anode 19 by a common conductor 30. The cathodes 25 and the anode 18, on the one hand, and the cathodes 26 and the anode 19, on the other hand, are inclined one with respect to the other so that the edges of the flames or plasmas 13 which are expelled from the multiple anodes 18 and I9 meet along a single line of flame 31. If these flames are suffciently close together, the line of flame 31 may be continuous and may form a sort of plasma blade. If necessary, powder may be injected in the zone of convergence of the flames by a plurality of nozzles in a hopper 32 located within the angle separating the two groups of cathodes-anode and shown in dotted lines in FIG. 7 for the purpose of not interfering with the lower portion of the installation in this figure. FIG. 8 illustrates in cross section the installation of FIG. 7 including the hopper 32.

Depending upon working conditions, the work 33 which may be metal if desired, may be moved in the direction of the arrow X.

In another embodiment, which is useful for instance when it is desired to create a short delivery of energy and move the point of application rapidly, the various arcs are struck at predetermined intervals of time, spaced for instance by one or several hundredths of a second and according to a predetermined sequence. Of course, the various arcs can be extinguished according to a sequence and a predetermined program. As an example, a device of this character may be used to provide successive tack welds.

When a device of this character is used for spraying, the material being sprayed is preferably brought to each nozzle by one of two channels. In this case it may be desirable to adjust the delivery of powder to each nozzle. Such devices make it possible to produce two or more plasma flames rather close together. These devices can of course be combined with the process described in Sunnen U.S. Pat. No. 3,205,338, granted Sept. 7, 1965 and Sunnen U.S. Patent No. 3,248,513, granted Apr. 26, 1966, both for Equipment For Forming High Temperature Plasmas (Belgian Pat. No. 623,2]8) by which alternating current is superimposed on direct current for maintaining the arc.

An example of a device of this character as shown in FIG. 9 can provide electric resistance heating of a strip 34 while in motion. Two cathode-anode multiple devices 35 and 36 are located at some distance from one another. Each of these devices comprises multiple anodes 18 and 19, and two groups of cathodes 25 and 26, each of which is electrically connected to one terminal of a direct current power source as shown, while the other terminals of these power sources are connected collectively to the respective anodes 18 or 19. Furthermore, the two sets of anodes 18 and 19 are connected respectively to the terminals of the secondary 37 of a high power alternating current transformer 22. The alternating current passes through each plasma flame emerging from each nozzle of one of the anodic groups, then across the strip 34 to be heated (moving in the direction of the arrow Y), returning to the transformer 22 by the corresponding plasma flames of the other anodic group. By such a device it is possible to heat the strip 34 while in motion by convection from each plasma flame on the one hand, and by PR electric heating effect ofthe alternating current on the other hand. This procedure makes it possible to apply a high electric current to work to be heated without requiring that an electric terminal connect to the work. This greatly simplifies the problem of electric resistance heating at high temperature. It can be used particularly for sintering strips obtained by cold rolling of powders while these strips are in motion. The current which passes through the work is double, that is, the superimposing alternating current which passes by the path of least impedance, and the direct current. It is possible to determine in advance, and to vary the distribution of both currents by varying the direct current and the gas output for each anode, thereby adjusting the electric resistance of each plasma flame through which the alternating current must pass.

In an embodiment used to spray very large outputs of material over sheets or strips, two sets of multiple anodes are used with their flames meeting at a distance of several millimeters from the anodes. Between the two sets of anodes, an alternating voltage is applied to create intense heating by the passage of the alternating current through the plasmas. The material to be sprayed is either brought into each nozzle, or between the two sets or anodes, or applied in both manners.

In usual forms of the invention all of the nozzles are parallel and extend in the same direction. However, to obtain a suitable thermal efiect, it may be preferable to orient the various nozzles differently and give them unequal dimensions. In fact,

I the arrangements of the nozzles may be different and one may use, for exam le, an annular multi le anode, in which the nozzles are paral el, as shown in FIG 10 and 11, all equidistant on a circumference in concentric fashion.

The installation shown by way of example in FIGS. 10 and 11 consists of three concentric rings 38, 39 and 40 attached together. The upper ring 38 is of a highly conductive metal, such as copper, and carries a set of eight cathodes 41 which are equidistant and concentric with respect to the ring. This ring is provided internally with channels 42 and 43 for circulation of cooling water. The lower ring 40 comprises a set of eight nozzles 44 corresponding respectively to the eight cathodes 41. They are surrounded with a common cooling chamber 45 for water circulation.

Between the rings 38 and 40 there is a third ring 39 made of insulating material, such as asbestos-phenolformaldehyde (Bakelite) and it is pierced by eight holes at equal distances from each other to permit the eight cathodes to pass through. On the sides of these holes, channels 46 are provided to bring in plasmagene gas to the chambers surrounding the cathodes. A device of the form shown in FIGS. 10 and 11 may be used to uniformly heat a mass to a very high temperature, such as when pulling monocrystals along the axis of the annular anode.

In another device of the invention as shown in FIG. 12, an annular anode 62 is used, where the axes of the nozzles and of the corresponding cathodes are radial. Installations of this character are useful for heating a bar 63 while in motion as for zone melting purification. The bar passes between the flames 13 at their zone of convergence.

As previously indicated, the thermal effect may be adjusted by modifying the shape of the nozzle, the output of gas through a particular nozzle, or the power applied to an individual are or group of arcs. Also, the spacing of the nozzles may be modified to obtain more or less energy density and in the case of multiple linear anodes, more energy can be applied at the center or at the ends if desired.

In view of our invention and disclosure, variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of our invention without copying the process and structure shown, and we therefore claim all such insofar as they fall within the reasonable spirit and scope of our claims.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. A process for treatment of an electrically conductive surface at high temperature, which comprises generating a first group of plasma jets projected on the surface generally sideby-side and approximately parallel to each other and impinging along a line on the surface, generating a separate second group of plasma jets generally side by side and approximately parallel to each other and impinging along the same line on the surface, the two separate groups differing from each other in the direction ofimpingement of the group ofjets so that the respective groups of plasma jets converge at that line on the surface, and passing electric current into the impingement zone and out of the impingement zone entirely through the plasma jets in the two groups rather than having any of the current pass in or out any other way and heating the material by the current in between.

2. A process of claim 1, in which the generating of each group of plasma jets includes generating pilot arcs from a pilot direct current electrical current in each of the plasma jets, and the current passed through for heating is a main current.

3. A process of claim 1, for overlaying, which comprises directing material for overlay of the surface to strike the surface along the line of impingement of the jets on the surface.

4. A process of claim 2, for overlaying, which comprises directing material for overlay of the surface to strike the surface along the line of impingement of the jets on the surface. 

1. A process for treatment of an electrically conductive surface at high temperature, which comprises generating a first group of plasma jets projected on the surface generally side-by-side and approximately parallel to each other and impinging along a line on the surface, generating a separate second group of plasma jets generally side by side and approximately parallel to each other and impinging along the same line on the surface, the two separate groups differing from each other in the direction of impingement of the group of jets so that the respective groups of plasma jets converge at that line on the surface, and passing electric current into the impingement zone and out of the impingement zone entirely through the plasma jets in the two groups rather than having any of the current pass in or out any other way and heating the material by the current in between.
 2. A process of claim 1, in which the generating of each group of plasma jets includes generating pilot arcs from a pilot direct current electrical current in each of the plasma jets, and the current passed through for heating is a main current.
 3. A process of claim 1, for overlaying, which comprises directing material for overlay of the surface to strike the surface along the line of impingement of the jets on the surface.
 4. A process of claim 2, for overlaying, which comprises directing material for overlay of the surface to strike the surface along the line of impingement of the jets on the surface. 